Unionist politicians have defeated a Sinn Féin bid to create marriage equality for gay couples in Northern Ireland. The votes of the Democratic Unionist party and Ulster Unionist party in the Stormont Assembly helped defeat a Sinn Féin motion backed by the SDLP, Alliance and the Green party.

But their defeat of the proposed bill sets the scene for a legal challenge in both the British and European courts against the continued ban on gay marriage in part of the UK.

Amnesty International today repeated a warning first made in the Guardian last month that the prospect of a a gay couple taking a legal case to the European Court of Human Rights is now a distinct possibility.

Sinn Féin Assembly member for South Down Caitriona Ruane said: "Attitudes in Ireland are changing because people do not want to see people discriminated against.

"The gay community has said enough is enough. They are standing up for themselves and their communities."

She claimed young people were turning to suicide by because of the taunts. "If they don't have an alternative voice to the vitriolic gay-bashing they will internalise it," she said.

Unionists were petitioned to oppose the legislation by not only the main Protestant churches but also the Catholic Church. But the gay Christian lobby group Changing Attitudes Ireland condemned the unionist veto on marriage equality.

Church of Ireland minister Canon Charles Kenny, the secretary of Changing Attitudes Ireland, said: "The year is drawing nearer when the love and justice expressed in the gospels will win out and sweep away the faith-based prejudice against gay and lesbian couples."

A total of 95 members of the Assembly voted: 42 in favour, including all the nationalists. Three unionists out of 50 voted yes, as did former Ulster Unionists Basil McCrea and John McCallister.

Democratic Unionist finance minister Sammy Wilson defended his party's veto and said colleagues would use it again to defeat "reckless" legislation.